Influence of Solvent Polarity on the Kinetics of Microwave-assisted Extraction, Composition, and Antiradical Activity of Black Locust Flowers (Robinia pseudoacacia flos) Extracts

I. M. Savic, I. A. Boskov and I. M. Savic Gajic

Abstract
The present study investigated the influence of solvent polarity on the kinetics of microwave-assisted extraction of phenolic compounds from black locust flowers. Extractions were conducted in an open-vessel microwave system operating at 462 W, with a constant liquid-to-solid ratio of 10 mL g–1. Extraction kinetics were simulated using Ponomarev’s model and an unsteady-state diffusion model. Furthermore, the effect of solvent polarity was evaluated with respect to the mineral composition and antiradical activity of the extracts.Among the tested solvents, the 50 % (v/v) ethanolic extract showed the highest total phenolic content (1.94 g gallic acid equivalents/100 g d.m.) and flavonoid content (0.97 g rutin equivalent/100 g d.m.), while simultaneously exhibiting the strongest antiradical activity (half-maximal inhibitory concentration of 0.424 mg mL–1). Correlation analysis indicated that the antiradical activity is not solely attributable to the presence of phenolic compounds, but also to other bioactive compounds present in the extracts. Solvent polarity significantly affected macro- and micro-element content, with potassium identified as the predominant macroelement. The absence of detectable heavy metals, specifically lead and cadmium, confirms the safety profile and suitability of the extracts for further application. The extracts, particularly those obtained using 50 % (v/v) ethanol, demonstrate significant potential as bioactive ingredients for functional product development. These findings support the replacement of synthetic additives with natural alternatives, aligning with the principles of sustainable and green chemistry.

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Keywords
Robinia pseudoacacia flos, microwave-assisted extraction, kinetics, phenolic compounds, mineral composition